Right Click and Hit the Tab Button
Right-clicking selects the object you want to edit (in this case, it would be your text), and the "tab" button on your keyboard (above caps lock) allows you to enter into Edit Mode. Alternatively, you could right-click on your text and then enter Edit Mode via the menu at the bottom of your screen where it says "Object Mode".

Check out this link and see if it helps: https://docs.blender.org/manual/en/dev/modeling/texts/editing.html